The present invention relates in general to ferrite shields for suppressing high frequency noise to and from cables and, in particular, to a new and useful ferrite suppressor case which includes fingers that engage a cable to be shielded, for firmly positioning the shield along the cable.
Ferrite suppressors are manufactured in geometries which use about one cubic inch of ferrous oxide material cast into various cylindrical or rectangular shapes. A hole is provided in the suppressor through which a cable or wire can pass. The cables which use this type of product are data transmission electronic circuits, usually processing frequencies from computer sources. Such a wire or cable can act as an antenna by either receiving or transmitting other unwanted frequencies.
Certain Federal Communications Commission (FCC) regulations require suppression or elimination of these unwanted frequencies. Also, many computer devices require the same type of suppression to enhance overall system performance. Ferrite shields installed on the cable suppress the higher, unwanted frequency signals while permitting the lower data frequencies to pass unaltered. Thus, the undesirable "antenna characteristic" of a cable is controlled.
An advancement to the original solid ferrite designs has been to split it in half, or bisect it. This allows the two halves to be jointed over the wire. A coarse and unsophisticated method of holding the halves together has been to simply tape or wrap them with a wire wrap tie.
U.S. Pat. No. 3,003,084 to Wilkinson discloses a grommet construction for passing cables having different diameters. The grommet is described as having a plurality of separate sectors which each taper downwardly to an apex so that a cable passing through the opening of the grommet tends to bend the thinner portion of the grommet. Thus, despite the diameter of the conductor, the grommet effectively isolates an enclosure to which the grommet is
U.S. Pat. Nos. 3,223,776 to Piasecki and 3,278,674 to Matthysee et al. show junction enclosing cases having slot shaped openings with a plurality of projections or comb like tines closely engage multiple conductors extending through the case, regardless of the diameters of the conductors.
U.S. Pat. No. 3,846,725 to Mears, Jr. discloses a case for enclosing an FM coil which has semicircular openings at opposite ends thereof with a plurality f outwardly included flexible projections for closely engaging a coil to be held in the case.
None of the foregoing prior art patents mentions the use of a ferrite core for engagement around a conductor.
U.S. Pat. No. 4,825,185 to Matsui shows a split ferrite core that is held in two halves of a case for snapping closed around a conductor to achieve a shielding function. Also see U.S. Pat. No. 3,924,223 to Whyte et al. which shows ferrite core halves for shielding a wire.